QUARTERLY FINANCIAL DATA (UNAUDITED) (Details)	3 Months Ended								12 Months Ended
	Dec. 31, 2016 USD ($) $ / shares $ / item	Sep. 30, 2016 USD ($) $ / shares $ / item	Jun. 30, 2016 USD ($) $ / shares $ / item	Mar. 31, 2016 USD ($) $ / shares $ / item	Dec. 31, 2015 USD ($) $ / shares $ / item	Sep. 30, 2015 USD ($) $ / shares $ / item	Jun. 30, 2015 USD ($) $ / shares $ / item	Mar. 31, 2015 USD ($) $ / shares $ / item	Dec. 31, 2016 USD ($) $ / shares $ / item	Dec. 31, 2015 USD ($) $ / shares $ / item	Dec. 31, 2014 USD ($) $ / shares
QUARTERLY FINANCIAL DATA (UNAUDITED)
Revenue	$ 12,745,657	$ 12,371,881	$ 12,254,264	$ 12,183,288	$ 12,133,802	$ 11,209,974	$ 11,061,418	$ 11,075,520	$ 49,555,090	$ 45,480,714	$ 42,632,319
Expenses	9,232,731	9,274,045	9,019,667	8,768,697	8,610,725	7,832,159	7,767,467	8,387,609	36,295,140	32,597,960	31,545,752
Income Before Other Income (Expense)	3,512,926	3,097,836	3,234,597	3,414,591	3,523,077	3,377,815	3,293,951	2,687,911	13,259,950	12,882,754	11,086,567
Other Expenses	(1,984,171)	(1,887,089)	(2,254,011)	(2,183,827)	(2,330,373)	(2,304,069)	(2,197,494)	(2,278,253)	(8,309,098)	(9,110,189)	(10,061,717)
Net Income	$ 1,528,755	$ 1,210,747	$ 980,586	$ 1,230,764	$ 1,192,704	$ 1,073,746	$ 1,096,457	$ 409,658	$ 4,950,852	$ 3,772,565	$ 1,024,850
Net Income per Unit before Discontinued Operations | $ / shares	$ 12.24	$ 9.69	$ 7.85	$ 9.84	$ 9.47	$ 8.51	$ 8.66	$ 3.22	$ 39.62	$ 29.86
Net Income per Unit (in dollars per unit) | $ / shares	$ 12.24	$ 9.69	$ 7.85	$ 9.84	$ 9.47	$ 8.51	$ 8.66	$ 3.22	$ 39.62	$ 29.86	$ 7.96
Income Per Depositary Receipt Before Discontinued Operations (in dollars per unit) | $ / item	0.41	0.32	0.26	0.33	0.32	0.28	0.29	0.11	1.32	1.00
Net Income Per Depositary Receipt (in dollars per receipt) | $ / item	0.41	0.32	0.26	0.33	0.32	0.28	0.29	0.11	1.32	1.00